A 23 year old woman with a closed head injury who developed rapidly fluctuating sodium levels.

CASE REPORT A 23-year-old woman was admitted to the intensive care unit (ICU) with a closed head injury. Her progress had been uneventful until day 11 when a nosocomial pneumonia developed which was treated with intravenous Timentin (ticarcillin sodium and potassium clavulanate) at a dose of 3.1 g in 100 mL of normal saline, 6-hourly. Later that day she had a large diuresis, raising the possibility of diabetes insipidus (DI). A venous blood sample was taken at 1600 hr. The plasma sodium concentration at this stage was 160 mmol/L, whereas earlier that day (i.e. 0600 hr) it had been 143 mmol/L (Table 1). As the results suggested the diagnosis of DI, a 5% dextrose infusion was commenced at a rate of 100 mL/hr. However, no further episodes of polyuria were observed and a repeat venous blood sample taken at 2100 hr revealed a plasma sodium of 123 mmol/L. As the patient’s neurological status had remained unchanged, the rapid change in the sodium values lead us to the most likely diagnosis. A venous biochemical analysis was performed at 0146 hr. The biochemical results throughout this period are shown in Table 1.